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United States Patent |
5,186,548
|
Sink
|
February 16, 1993
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Bearing shaft seal
Abstract
A seal assembly for sealing an annular space between a housing having a
cylindrical bore therein and a shaft member extending into and mounted for
coaxial rotation relative to the bore, includes a resilient sealing body
having an annular lubrication sealing lip and a dust seal including first
inwardly directed resilient dust sealing lip having an inside diameter
less than the diameter of the shaft member for contacting the shaft member
and forming a primary dust seal therewith and a second inwardly extending
annular dust seal lip between the first dust seal lip and the second dust
seal lip having an inside diameter slightly greater than the diameter of
said shaft member to form a non-contacting type seal with the other
surface of the shaft member.
Inventors:
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Sink; Danny R. (Richmond, VA)
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Assignee:
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Brenco, Incorporated (Petersburg, VA)
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Appl. No.:
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832238 |
Filed:
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February 7, 1992 |
Current U.S. Class: |
384/486; 277/568 |
Intern'l Class: |
F16C 033/78; F16J 015/32 |
Field of Search: |
384/477,484,486
277/153
|
References Cited
U.S. Patent Documents
4243232 | Jan., 1981 | Repella | 277/153.
|
4278261 | Jul., 1981 | Miura et al. | 277/153.
|
4336945 | Jun., 1982 | Christiansen et al. | 277/153.
|
4432557 | Feb., 1984 | Drucktenhengst | 277/153.
|
4550920 | Nov., 1985 | Matsushima | 277/153.
|
4721312 | Jan., 1988 | Hornberger | 277/37.
|
4747603 | Mar., 1988 | Sugino et al. | 277/26.
|
4799808 | Jan., 1989 | Otto | 384/486.
|
4848776 | Jul., 1989 | Winkler | 384/436.
|
4987826 | Jan., 1991 | Deppert et al. | 92/168.
|
5037213 | Aug., 1991 | Uchida et al. | 384/484.
|
5083802 | Jan., 1992 | Shimasaki et al. | 277/152.
|
Foreign Patent Documents |
867005 | May., 1961 | GB | 384/486.
|
Primary Examiner: Hannon; Thomas R.
Attorney, Agent or Firm: Kerkam, Stowell, Kondracki & Clarke
Claims
What is claimed is:
1. A rail car wheel bearing seal assembly for sealing an annular space
between a wheel housing having a cylindrical bore therein and an axle
member extending into the base and having a bearing mounted thereon
supporting the wheel for rotation thereon, the sealing assembly including
a rigid support ring having a generally cylindrical body portion adapted
to be received and supported in the cylindrical bore in fluid-tight
relation therewith, and a resilient ring-shaped sealing body mounted on
said support ring in position to contact and form a fluid seal around the
outer surface of the axle member, said resilient sealing body including an
annular lubrication sealing lip adapted to contact the axle around its
periphery and low friction dust seal means axially spaced from said
lubrication sealing lip, said dust seal means comprising
a single annular, resilient primary dust seal lip having an inside diameter
less than the diameter of said shaft member for contacting the shaft
member and forming a primary dust seal therewith,
a single annular, annular secondary dust seal lip between said primary dust
seal lip and said lubrication sealing lip, said secondary dust seal lip
having an inside diameter slightly greater than the diameter of said shaft
member whereby when the seal assembly is mounted on said housing said
secondary dust seal lip will form a non-contacting seal with the outer
surface thereof,
a first annular recess in said resilient body between said primary and said
secondary dust seal lips, said first annular recess in combination with
the shaft member providing a first annular cavity spaced axially from said
lubrication sealing lip,
the ratio of the axial distance between said lubrication sealing lip and
said secondary dust seal lip to the distance between said secondary dust
seal lip and said primary dust seal lip being at least 4 to 4,
said resilient sealing body having an annular concave inner surface between
said secondary dust seal lip and said lubrication sealing lip, said
concave surface cooperating with the outer surface of the shaft member to
define a second annular cavity extending between said secondary dust seal
lip and said lubrication sealing lip,
said resilient sealing body being molded from a single homogeneous mass of
elastomeric material having a durometer hardness within the range of 73 to
90,
the difference between the diameter of said secondary dust seal lip and the
diameter of the shaft member being within the range of about 0.001 to
about 0.008 inches.
2. The seal assembly defined in claim 1 wherein said resilient sealing body
is molded from a single homogeneous mass of elastomeric material having a
durometer hardness within the range of 73 to 80.
3. The seal assembly defined in claim 1 wherein the difference between the
diameter of said second dust seal lip and the diameter of said shaft
member is within the range of about 0.002 to about 0.005 inches.
4. The seal assembly defined in claim 1 wherein said second annular cavity
has a volume substantially greater than said first annular cavity.
5. The seal assembly as set forth in claim 1 wherein said first and said
second dust seal lips are outwardly directed with respect to said annular
cavity.
Description
BACKGROUND OF THE INVENTION
2. Field of the Invention
This invention relates to bearing shaft seals and more particularly to such
a seal including an elastomeric seal body having a lubricant sealing
portion and an improved dust sealing portion spaced axially from the
lubricant sealing portion.
2. Description of the Prior Art
It is well known to provide lubricant seals between a shaft and a
cylindrical housing within which the shaft is supported for rotation
relative to the housing, with the seal consisting of a rigid support ring
adapted to fit in fluid-tight relation within a cylindrical bore in the
housing. The ring supports a resilient rubber-like sealing element in
fluid-tight contact with the outer surface of the relatively rotating
shaft or a wear ring supported thereon. Examples of such seals are shown
in U.S. Pat. Nos. 4,747,603 and 4,278,261. When seals of this type are
operated in an environment where foreign matter such as dust, mud or water
may contact the outer surface of the resilient sealing element, it is
common practice to provide a secondary seal usually referred to as a dust
lip or auxiliary lip, in an attempt to prevent the ingress of such foreign
material (dust) into the sealed area between the housing and shaft. Seal
assemblies including dust seals of this general type are shown, for
example, in U.S. Pat. Nos. 4,243,232; 4,278,261; 4,336,945; and 4,721,312.
While the prior art bearing shaft seals incorporating dust lips have
generally been satisfactory for most uses, they have not been entirely
satisfactory for use in environments containing heavy concentrations of
abrasive and corrosive dust, particularly where inspection of the seal and
related equipment cannot readily be made during operation. For example,
the wheels on railroad cars are supported on the car axles or shafts for
rotation by low friction roller bearings, with seals provided at each end
of each wheel bearing to prevent the escape of the grease or oil used to
lubricate the bearing and to prevent ingress of contaminants. Such seals
are subject to constant and severe vibration while the car is being
transported and continuously operate in a hostile environment where dust
and corrosive materials from the product hauled, as well as dust, mud and
water from the roadbed, present a serious problem because of the tendency
of abrasive and corrosive materials to find their way past the seal and
contaminate the lubricant. Such contaminant materials tend to be very
abrasive to the shaft and/or wear ring, causing premature wear and
failure, with the consequent danger of accelerated dust penetration or
lubrication loss and damage to the sealed bearing structure.
As pointed out in the above-mentioned U.S. Pat. No. 4,336,945, seals of
this type generally employ a so-called hydrodynamic or pumping surface
contour in the area of the primary lubricant sealing lip, which pumping
surface tends to pump or impel escaping oil back into the sealed area. Any
dust particles or the like which penetrate past the dust seal portion may
actually be entrained in escaping oil adjacent the primary lubrication
sealing area and be pumped back into the sealed bearing cavity. The
abrasive action of even small amounts of such dust can increase the
bearing friction, thereby causing overheating of the lubricant and
ultimate failure of the bearing.
Attempts to solve the problem of dust penetration include providing dual
dust lips spaced axially from one another, with the lips dimensioned to
contact the shaft and to be deflected outwardly away from the lubricant
seal portion when the seal is installed. It should be apparent, however,
that where a seal is employed at each end of a bearing which is mounted
from one end of an axle or shaft, the desired outwardly deflected
arrangement of the dual dust seal lips disclosed in this patent cannot
always be assured. Further, a double sealing lip continuously contacting
the shaft increases the friction load which not only requires additional
power or energy, but also results in additional heat which can result in
an overheating of the seal and premature or accelerated degeneration of
the elastomer. Heat from seals are a known contributing factor or cause of
many hot boxes on rail cars. Even where the temperature of the bearing is
not elevated to a dangerous condition, the temperature may rise
sufficiently to cause a premature warning to be given from a hot box
detector causing a railcar to be unnecessarily pulled from service.
In the normal operation of low friction roller bearings such as used to
mount a wheel on a rail car axle, some small amount of lubricant will
inevitably leak past the primary lubricant seal lip. Some leakage is
desirable to wet the primary lip, and such leakage generally is minimized
and controlled by a combination of features including the use of
compression members such as an endless coil garter spring ring employed to
continuously resiliently urge the lubricant sealing lip into contact with
the rotating shaft and the use of the above-mentioned hydrodynamic surface
contour on the resilient primary lubricant sealing lip.
Any lubricant weepage past the dust lip will quickly become contaminated
with dust particles and will tend to build up on the shaft outwardly
adjacent the dust lip. Entrainment of substantial dust particles causes
the contaminated lubricant to become abrasive and wear the shaft or wear
ring and, to a much lesser extent, the resilient sealing element with
which it is in rubbing contact. Such seal and/or shaft ring wear reduces
the efficiency of the dust shield and increases the likelihood of ingress
of contamination through the primary lubricant seal into the sealed
bearing area. Also, ingress of dust particles will ultimately increase
wear on the primary lubricant sealing surface and clog the hydrodynamic
feature referred to above.
It is, therefore, a primary object of the present invention to provide an
improved bearing shaft seal assembly.
Another object is to provide a shaft seal element which includes improved
dust sealing features.
Another object is to provide such a sealing element including a primary
lubricant sealing area and axially spaced dust sealing area, with the dust
sealing area including both a shaft contacting and a non-contacting lip to
improve the dust sealing qualities of the assembly.
Another object of the invention is to provide an improved wheel bearing
seal assembly for heavy duty vehicles having improved sealing qualities
and longer service life.
SUMMARY OF THE INVENTION
In the attainment of the foregoing and other objects, an important feature
of the invention resides in providing a low friction seal employing a
double dust lip seal which is highly effective in preventing the ingress
of dust particles into the sealed area. This is accomplished by providing
a primary and a secondary dust sealing lip, i.e, a double dust lip, with
the primary dust sealing lip and secondary dust sealing lip being located
axially outward from the primary or main lubricant sealing lip and with
the primary dust sealing lip dimensioned to be in continuous rubbing or
sealing contact with the outer surface of the relatively rotating shaft
element and the inner or secondary dust sealing lip located axially inward
of the primary dust sealing lip and dimensioned to be in closely spaced
relation to but not in rubbing contact with the shaft element.
The primary and secondary dust sealing lips are dimensioned such that the
outer primary dust lip is relatively flexible while the inner or secondary
dust lip provides greater rigidity or stability to thereby maintain the
close tolerance spacing with the shaft. The secondary dust sealing lip
operating out of contact with the shaft element has been found to
substantially reduce the ingress of dust particles into the area outward
of and adjacent to the primary lubricant sealing surface of the seal body.
As a consequence, the ingress or pumping of contaminated oil into the
sealed area of the bearing by the hydrodynamic surface on the seal is
substantially reduced. It is believed that dust particles which find their
way past the primary dust seal lip tend to become entrained in lubricant
used to pack or pre-lube the seal or which has weeped from the sealed area
and which has found its way to the area between the primary and secondary
dust sealing lips. Thus, the more heavily contaminated lubricants in the
cavity area are concentrated between the primary and secondary dust
sealing lips. Further, the non-contacting secondary dust sealing lip has
less tendency to wear and therefore maintains its enhanced dust sealing
effect over a greater period of time.
BRIEF DESCRIPTION OF THE DRAWING
Other features and advantages of the invention will be apparent from the
detailed description contained hereinbelow, taken in conjunction with the
drawings, in which:
FIG. 1 is an enlarged fragmentary sectional view of a portion of a rail car
wheel bearing and shaft embodying the improved seal of the present
invention; and
FIG. 2 is a further enlarged view of a portion of the seal structure shown
in FIG. 1.
DESCRIPTION OF THE PREFERRED EMBODIMENT
Referring now to the drawings in detail, an improved seal assembly in
accordance with the present invention is designated generally in FIG. 1 by
the reference numeral 10 and it is shown installed for use in connection
with a low friction rail car wheel bearing assembly indicated generally by
the reference numeral 12. The bearing assembly includes an outer housing
or cup member 14 having a cylindrical recess 16 formed in its open end for
receiving the seal assembly 10, and races for the bearing elements 18
which, in turn, rotate on the bearing surface of inner race ring members
20.
The seal assembly 10 comprises a rigid support ring 22 having mounted on
its inner periphery a resilient sealing element indicated generally at 24.
Support ring 22 includes a large diameter open ended section 26 adapted to
fit in sealing relation within the cylindrical bore 16 to rigidly but
releasably retain the seal on the bearing An enlarged retaining lip 28
formed on the end of cylindrical portion 26 is adapted to snap into an
undercut groove 30 in the cylindrical bore 16 to retain the seal assembly
on the bearing
A smaller diameter cylindrical body portion 32 of the support ring 22
extends outwardly from the bearing 12 and is joined to portion 26 by a
radial segment 34. Ring 22 terminates at its end spaced from the bearing
assembly 12 in an inwardly directed flange portion 36 having an inturned
lip 38 for supporting the resilient seal element 24. Seal element 24 is
molded on and is permanently bonded to the rigid metallic ring 22 in a
manner well known in the art.
In the embodiment illustrated in the drawings, the bearing and seal
assembly is supported on the cylindrical shaft or axle 40 of the rail car,
and a wear ring or spacer element 42 engaging the end of the inner race
element 20 axially fixes the bearing and seal on the shaft 40. Wear ring
42 preferably is formed from a harder, more wear resistant material than
shaft 40, and may be replaced when worn or damaged, as necessary. A
retaining cap 44 is rigidly mounted on the end of the shaft by bolt means,
not shown, with the cap 44 engaging the end of the wear ring 42 to firmly
clamp the wear ring and the bearing inner race on the shaft. Thus, the
wear ring 42 becomes, in effect, an integral part of the shaft with inner
surface of the wear ring and shaft being in fluid-tight sealing relation.
As seen in FIG. 1, the sealing element 24 contacts the outer cylindrical
surface 58 of the wear ring 42 to provide the desired seal to maintain the
lubricant within the bearing and the sealed spaced indicated generally at
46. It should be apparent, however, that the wear ring may be omitted and
the seal formed directly between the sealing element 24 and the outer
surface of the shaft 40.
The seal element 24 is preferably integrally molded from a single mass of
homogeneous rubber-like material preferably having a durometer hardness
within the range of about 73 to 80 and for most applications should not
have a hardness exceeding a 90 durometer reading. The seal body 24 is a
continuous annular ring having an inner primary lubricant sealing area at
its free end, i.e., the end spaced from the support lip 38. As shown in
FIG. 2, the primary lubrication sealing area is defined by a lubricant
sealing lip 50. A contoured hydrodynamic surface is formed on the
outwardly directed surface of the lip 50 with this hydrodynamic or pumping
surface being indicated by the surface contours 52. As indicated
previously, such hydrodynamic pumping surfaces are known in the art and as
such forms no part of the present invention. Preferably, a resilient
compression element such as the endless coil spring or garter spring 54 is
supported on an outwardly directed groove radially outward from the lip 50
to maintain a continuous, controlled sealing pressure between the sealing
lip 50 and the outer sealing surface 58 of the wear ring 42.
At its opposite or outer end, the elastomeric body is provided with a dust
seal in the form of a double dust lip including a primary outwardly
directed dust lip 60 and an axially inwardly spaced, outwardly directed
secondary dust lip 62 at locations generally radially inward from the end
flange portion 36 of the metallic support ring. The seal body 24 has a
concave inner surface 64 between sealing lips lips 60 and 62 which,
together with the outer surface 58 of the wear ring 42, defines an annular
cavity or pre-lube chamber 66 when the seal is installed. A second annular
chamber or cavity 68 is provided between the adjacent surfaces of dust
seal lips 60 and 62 and the wear ring surface 58. In practice, the
chambers 66 and 68 will be filled or packed with a lubricant prior to
installing the seal on the shaft or wear ring, whereby the seal is
prelubricated. The lubricant used to pack the seal may be different than
but must be compatible with the lubricant used in the sealed bearing.
The axial spacing between the primary lubrication sealing lip 50 and the
secondary dust seal lip 72 is substantially greater than the distance
between the first and second dust seal lips 70 and 72, respectively, and
similarly the size of the cavity 66 is substantially larger than the
volume of cavity 68. The ratio of the distance between lip 50 and lip 62
to the distance between lips 60 and 62 should be at least 4 to 1 and
preferably at least 6 to 1.
As indicated by the broken line in FIG. 2, the diameter of the outer
surface 58 of wear ring 42 will, when the seal is installed, deflect or
deform the inner sealing edge 70 of lip 60 outward to maintain continuous
rubbing contact; however, the corresponding inner edge 72 of the secondary
dust seal lip 62 will be spaced from the surface 58 In practice, it is
desired that the difference between the diameter of the secondary dust
seal lip and the diameter of the shaft member be maintained as low as
practical to produce an effective seal therebetween without resulting in
actual rubbing contact. It has been found that this difference should be
within the range of about 0.001 to 0.008 inches, and preferably about
0.002 to 005 inches. In contrast, the primary dust seal should be
deflected outward by the shaft member to increase its diameter by about
0.003 to 0.018 inches, and preferably about 0.008 to 0.013 inches.
Tests have been conducted to compare the efficiency of the seal according
to the present invention with a similar seal design but without the
secondary dust seal lip. These tests have shown that contamination of the
lubricant in the sealed area, i.e., inward of the primary lubricant seal,
may be reduced by as much as 60% by use of the secondary, non-contacting
dust seal lip. At the same time, the non-contact sealing feature of the
secondary dust seal lip does not increase the torque load of the seal.
It is not known precisely how the non-contacting secondary dust seal lip
functions to reduce the contamination of the bearing lubricant. It is
believed however, that dust particles which find their way past the
primary dust seal lip into the annular chamber 68 initially become
entrained in the lubricant which acts somewhat like a stuffing box to
isolate and retain the contaminated lubricant primarily in chamber 68 so
that less contamination or dust reaches the area of the primary lubricant
seal where it can be pumped back into the bearing by the hydrodynamic seal
surface described hereinabove. Regardless of the precise manner in which
the seal functions, the unique design is extremely effective in preventing
the ingress of dust into the sealed area of the bearing, and this is
accomplished without increased friction.
It is known that friction from commercially available lubricant seals
employed on rail cars provide substantial rolling resistance. This is
particularly true when initially starting a car from the rest position
where up to one horsepower may be required to overcome the initial
friction of each of the 16 seals employed to seal the 8 wheel bearings of
a rail car. Thus, at least in theory, the train locomotive would have to
apply 1600 horsepower just to overcome the rolling resistance of the wheel
bearing seals to start a 100 car train. Once the train is in motion, a
lesser but significant amount of power is still required to continuously
overcome the bearing seal friction. Thus, elimination of a continuous
rubbing seal surface in accordance with the present invention may result
in substantial energy savings over seals employing two dust seal lips in
continuous rubbing contact with the shaft.
While a preferred embodiment of the invention has been disclosed and
described, it should be understood that the invention is not so limited
but that it is intended to include all embodiments which would be apparent
to one skilled in the art and which come within the spirit and scope of
the invention.
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